1. Field of the Invention
This invention relates to a method of manufacturing a pressure control valve, more particularly to improvements in a method of manufacturing a valve seat surface in this pressure control valve, and for example, a method of manufacturing a pressure control valve, which is effective for use in techniques for manufacturing a fuel pressure control valve for controlling a fuel supply flow rate in accordance with fuel pressure.
2. Related Art Statement
In general, in a vehicle such as a motor vehicle, there has been used a fuel pressure control valve provided with a housing produced by die casting in a fuel supply path for delivering fuel in a fuel tank to an engine.
In the housing this type in the fuel pressure control valve, the housing constituting a control valve chamber together with a diaphragm is formed with a fuel introduction path and a fuel discharge path, which are communicated with the control valve chamber, and a valve body is mounted to the inlet side of the fuel discharge path. It is known a valve body using a ball (spherical valve body) as this valve body (Refer to Japanese Utility Model Laid-Open No. 3-17486 and U.S. Pat. No. 4,936,342 for example).
In the fuel pressure control valve in which the ball is used as the valve body, when the ball as being the valve body is mounted in the fuel discharge path, the ball is tightly attached to a valve seat surface to secure the sealing property, so that it becomes necessary to form a concave spherical seat valve surface on a valve body mounting portion of the fluid discharge path.
Then, with the method of manufacturing the pressure control valve of this type, in general, it is conceived that, when the valve seat surface is formed in the fuel discharge path, a spherical jig having the same shape as the ball is inserted into the valve body mounting portion, whereby the jig is punched to form the concave spherical surface on a contact surface between the jig and the valve body mounting portion.
However, with the method of manufacturing the pressure control valve of this type, there is such a risk that, when the jig is worn out, the shape of the jig becomes different from the shape of the ball as being the spherical valve body, whereby, even if the jig is punched, the sealing property may be lowered. Because of this, punching should be made while the shape of the jig is measured constantly, so that cost is required for the maintenance of the jig. Furthermore, cost is required for manufacturing the jig itself.
Furthermore, with the fuel pressure control valve this type, when the jig is punched to form the concave spherical seat valve surface on the contact surface between the jig and the valve body mounting portion, burrs inwardly directed in the radial direction may be produced on an end portion of the valve seat surface. These burrs are brought into a state of being projected into a path of a valve spring for biasing the ball toward a diaphragm, whereby such a case may occur that the burrs are raised to the ball side by the valve spring. When the burrs are raised to the ball side as described above, the forward ends of the burrs are projected farther than the seat valve surface. When the burrs are brought into the state of being projected as described above, contact between the ball and the valve seat surface is interfered by these burrs, whereby an interval occurs between the ball and the valve seat surface, so that the sealing property is lowered.